Moving thermal gradients in gas chromatography

• Model predicts GC solute band widths narrow with increases in thermal gradient slope.
• Predicted injection/stationary phase band broadening reduced with moving gradients.
• Predicted thermal gradient effects realized within the first 40–70 cm of the column.

This paper examines the separation effects of a moving thermal gradient on a chromatographic column in gas chromatography. This movement of the gradient has a focusing effect on the analyte bands, limiting band broadening in the column. Here we examine the relationship between the slope of this gradient, the velocity of the gradient and the resulting band width. Additionally we examine how transport of analytes along the column at their analyte specific constant temperatures, determined by the gradient slope and velocity, affects resolution. This examination is based primarily on a theoretical model of partitioning and transport of analyte under low concentration conditions. Preliminary predictions indicate that analytes reach near constant temperatures, relative positions and resolutions in less than 100 cm of column transport. Use of longer columns produces very little improvement in resolution for any fixed slope. Properties of the thermal gradient determine a fixed solute band width for each analyte. These widths are nearly reached within the first 40–70 cm, after which little broadening or narrowing of the bands occur. The focusing effect of the thermal gradient corrects for broad injections, reduces effects of irregular stationary phase coatings and can be used with short columns for fast analysis. Thermal gradient gas chromatographic instrumentation was constructed and used to illustrate some characteristics predicted from the theoretical results.